The Acrosome Reaction

The acrosome reaction is a change in the sperm that is common to many
higher animals. In the sea urchin, contact with egg jelly initiates the
acrosome reaction, which is a calcium-mediated process. The animations linked
to this page are courtesy of Dr. David
Epel at Stanford University's Hopkins Marine Station. In response to
signals presumably transduced by receptors on the surface of the sperm that
bind to components of egg jelly (red), actin polymerizes from a pool of
globular actin (pink) to form the acrosomal process. The acrosomal vesicle
(green) fuses with the plasma membrane, releasing enzymes from the tip of
the sperm that aid digestion of egg jelly. At the same time, bindin (blue)
is deposited on the surface of the acrosome-reacted sperm.